A large number of different intrauterine devices have been proposed and applied in practice. The first IUDs that became generally used were large and extended the uterus and caused bleeding and pain, often accompanied by infections. There have been several attempts to overcome the disadvantages related to the intrauterine systems, and devices have been designed with modifications aiming to decrease pain and bleeding, to make insertion and removal easier, to limit the risk of expulsion and especially to minimize the risk of perforation.
Applicant's patent application FI 20085277 relates to an intrauterine delivery system comprising a frame and a reservoir connected to the frame, wherein the frame forms a continuous, closed and flexible system of polygonal, preferably triangular or pentagonal, shape and wherein at least one end of the reservoir is connected to the inner surface of the frame and the reservoir comprises at least one therapeutically active substance.
EP 0873751 by Takeda Chemical Industries discloses a biodegradable IUD wherein an active agent is dispersed in a biodegradable polymer which is mould to a predetermined shape of a ring. Said IUD does not comprise separate frame and reservoir structures. As such systems are usually hard and inflexible, introduction of rings made of such material to the human body is very difficult. If the ring-like structure of the device is broken during the degradation process, it would be extremely difficult to remove the device because it would be deformed and its hard, broken parts would cause tissue damage.
NL 8601570 by Futura Nova relates to an intrauterine device comprising an elongated stem which is combined to a ring of polymeric material. A contraceptive effect is achieved by covering the stem with a contraceptive material, preferably with metal and especially with copper in the form of a ring spiral on the stem. Said device does not comprise a separate reservoir consisting of a polymer matrix or polymer layer capable of controlling the release of the contraceptive material. Therefore the release rate of said contraceptive material could not be controlled but would depend on the solubility characteristics of the contraceptive.
GB 1,318,554 by Michael Reese Hospital & Medical Center describes an intrauterine device comprising at least one capsule containing a progestin contained within a partially permeable wall but not dispersed in any polymer matrix. In one embodiment the device comprises three silicone elastomer tubes containing progestin and joined by polyethylene corner pieces to form a generally ring shaped or triangular device. The device is said to have sufficient rigidity to maintain its shape when not subjected to outside forces, but still be easily flexed as required for insertion. However, although the ends of the silicone tubes need not to be sharp, it is likely that they irritate uterine wall thus impairing wearing comfort.
Many of the devices presented in the literature are bulky and/or rigid and may therefore cause side-effects and a high discontinuation rate. Undesirable complications that have been associated with the use of these intrauterine devices are pain and difficulties in insertion and/or in removal of the device, abdominal pain, infection, irregular bleeding, hormonal side effects, uterine perforation, cervical laceration, septic abortion, ectopic pregnancy, and expulsion of the IUS.
The optimal performance of an intrauterine system has been found to be determined largely by the interaction of the geometric parameters of the uterus and the device. The uterine cavity possesses a single axial and variable transverse and anteroposterior dimensions. Cyclic changes in uterine shape and size occur normally in women during different phases of the menstrual cycle. An ideal intrauterine system should be able to functionally adapt to the cyclic variations of the uterine cavity. Larger size of an IUD has been stated to increase the risk of expulsion and side effects. Abnormalities in uterine geometry as a result of congenital or acquired space-occupying lesions reduce the uterine space available for IUDs and increase further the probability of IUD expulsion and other clinical complications. The devices that are designed to fit to the size of the endometrial cavity are expected to have better performance records than those inserted at random, causing less irritation and less side effects (Kurz, Contraception. 1984 Jun. 29(6):495-510) and producing less endometrial trauma and consequently less bleeding (Randic, Contracept Deliv Syst. 1980; 1(2):87-94). The shape of the IUD should have blunt surfaces and gentle curves, and be devoid of sharp features which may cause uterine injury. Axial stiffness and transverse flexibility of the device appear to improve compliance properties (Hasson, BJOG, 89 (s4), 1-10, 1982).
In addition to dimensions and design characteristics material properties are important for an ideal intrauterine system.
With the devices where during the insertion procedure at least part of the device is outside the inserter tube, insertion pain is related to the outer diameter, design and flexibility of the insertion tube, but also to the size, design and flexibility of the device, especially of the part of the device laying outside the insertion tube. Pain soon after insertion usually occurs in the form of uterine cramps, and is probably related to uterine distention or irritation of the isthmic region caused by the device. The pain or discomfort is rarely present for more than the first weeks after the insertion.
It is also well known that the uterus contracts with a certain frequency continually and the contractions can push the device downward causing partial or complete expulsion. The contraction of the uterus will bring pressure on the inserted device. The transverse composition of forces will deform the device, and the longitudinal composition of forces will expel the device.
Therefore the material should be flexible but have a relatively high degree of stiffness (measured according to DIN 53504), preferably >8 N/mm2 (at 100% elongation), especially more than 10 N/mm2 (at 100% elongation). The material should also have a relatively high hardness (measured according to DIN 5305), preferably Shore D>38 and <60, more preferably Shore D>40 and <55). Moreover the material should have a high rebound (measured according to DIN 53512), preferably >30%, especially more than 35%. The cross section thickness must be sufficiently high to provide wanted resilience in use, and this depends on the material used. However, the stiffness and the thickness must not be so high as to prevent the device, the core, the frame or both from being bent through a substantial angle in use. Furthermore, it is important that the materials have a relatively high elasticity and characteristics which permit the device to be deformed and then again to return to its original configuration upon release of the deforming force.
Correct insertion, with the IUD placed up to the fundus, is thought to reduce the chances of expulsion and proper position of the device is necessary to achieve the optimal contraceptive efficacy.
Despite of the development work done, many intrauterine systems still have drawbacks. To overcome the issues related to various side effects described above and to improve patient compliance, intrauterine systems comprising a new material with excellent performance have been introduced. The intrauterine systems according to present invention can be easily inserted in the stable optimal position in the uterus and are comfortable to use. They are flexible and have a smooth shape to minimize the risk of perforation, but still with low possibility for expulsions, and do not have any pain causing elements or structural features.